if (GetIQ() is < 100 and > 50)
    Console.WriteLine("Hoi polloi");

if (GetIQ() is < 100 and > 50 and var iq)
    Console.WriteLine("Hoi polloi IQ: {0}", iq);

var bicycle = TryGetBicycle();
if (bicycle != null)
    Console.WriteLine("Bicycle owner is {0}.", bicycle.Owner);

if (TryGetBicycle() is not null and var bicycle)
    Console.WriteLine("Bicycle owner is {0}.", bicycle.Owner);

var bicycle = TryGetBicycle();
if (bicycle != null)
{
    Console.WriteLine("Bicycle owner is {0}.", bicycle.Owner);
}
else
{
    var motorcycle = TryGetMotorcycle();
    if (motorcycle != null)
    {
        Console.WriteLine("Motorcycle owner is {0}.", motorcycle.Owner);
    }
    else
    {
        var car = TryGetCar();
        if (car != null)
        {
            Console.WriteLine("Car owner is {0}.", car.Owner);
        }
        else
        {
            // ... намученный баян который идет глубоко вниз и конкретно долбит мозг на 5-7-м уровнях вложенности ...
        }
    }
}

if (TryGetBicycle() is not null and var bicycle)
    Console.WriteLine("Bicycle owner is {0}.", bicycle.Owner);
else if (TryGetMotorcycle() is not null and var motorcycle)
    Console.WriteLine("Motorcycle owner is {0}.", motorcycle.Owner);
else if (TryGetCar() is not null and var car)
    Console.WriteLine("Car owner is {0}.", car.Owner);
else
    // ... красота на любом уровне "вложенности"! ...

int i = int.Parse(Console.ReadLine());

if (i == 1 || i == 3 && !(i == 5 && i != 5))
    Console.WriteLine(1);

if (i is 1 or 3 and not (5 and not 5))
    Console.WriteLine(2);

        public static bool Any<TSource>(this IEnumerable<TSource> source)
        {
            if (source == null)
            {
                ThrowHelper.ThrowArgumentNullException(ExceptionArgument.source);
            }

            if (source is ICollection<TSource> collectionoft)
            {
                return collectionoft.Count != 0;
            }
            else if (source is IIListProvider<TSource> listProv)
            {
                // Note that this check differs from the corresponding check in
                // Count (whereas otherwise this method parallels it).  If the count
                // can't be retrieved cheaply, that likely means we'd need to iterate
                // through the entire sequence in order to get the count, and in that
                // case, we'll generally be better off falling through to the logic
                // below that only enumerates at most a single element.
                int count = listProv.GetCount(onlyIfCheap: true);
                if (count >= 0)
                {
                    return count != 0;
                }
            }
            else if (source is ICollection collection)
            {
                return collection.Count != 0;
            }

            using (IEnumerator<TSource> e = source.GetEnumerator())
            {
                return e.MoveNext();
            }
        }

A>if (GetIQ() is < 100 and > 50 and var iq)
A>    Console.WriteLine("Hoi polloi IQ: {0}", iq);
A>

A>if (var iq = GetIQ() is < 100 and > 50)
A>    Console.WriteLine("Hoi polloi IQ: {0}", iq);
A>

if (TryGetBicycle(out var bicycle))
...
else if (TryGetMotorcycle(out var motorcycle))
...
else
...

_value1 = value1 ?? throw new ArgumentNullException(nameof(value1));
_value2 = value2 ?? defaultValue2;

var value = root?.child1?.child2;

if (value != null)
{
...
}

A>if (TryGetBicycle() is not null and var bicycle)
A>    Console.WriteLine("Bicycle owner is {0}.", bicycle.Owner);
A>

if (TryGetBicycle() is {} bicycle) ...

S>int i = int.Parse(Console.ReadLine());

S>if (i == 1 || i == 3 && !(i == 5 && i != 5))
S>    Console.WriteLine(1);

S>if (i is 1 or 3 and not (5 and not 5))
S>    Console.WriteLine(2);

S>int i = int.Parse(Console.ReadLine());

if (i == 1 || i == 3)
    Console.WriteLine(1);

if (i is 1 or 3)
    Console.WriteLine(2);

A>var vehicle = TryGetBicycle() ?? TryGetMotorcycke() ?? TryGetCar();
A>

Console.WriteLine("The owner is {0}.", TryGetBicycle()?.Owner ?? TryGetMotorcycle()?.Owner ?? GetDefaultValue().Owner);

A>var bicycle = TryGetBicycle();
A>if (bicycle != null)
A>    Console.WriteLine("Bicycle owner is {0}.", bicycle.Owner);
A>

A>if (TryGetBicycle() is not null and var bicycle)
A>    Console.WriteLine("Bicycle owner is {0}.", bicycle.Owner);
A>

if (var bicycle = TryGetBicycle(); bicycle != null)
    Console.WriteLine("Bicycle owner is {0}.", bicycle.Owner);

C>if (var bicycle = TryGetBicycle(); bicycle != null)
C>    Console.WriteLine("Bicycle owner is {0}.", bicycle.Owner);
C>

C>

if ((var bicycle = TryGetBicycle()) != null)
    Console.WriteLine("Bicycle owner is {0}.", bicycle.Owner);

List<Item> values ...;
List<Item> otherValues ...;
if (values.Any(item => длинное_условие_ && !otherValues.Contains(item)))
{
  Item item = values.First(то_же_самое_выражение_что_в_Any);
  ...
}

K>if (TryGetBicycle(out var bicycle))
K>

var vehicle = TryGetBicycle() ?? TryGetMotorcycke() ?? TryGetCar();

C>if (var bicycle = TryGetBicycle(); bicycle != null)
C>    Console.WriteLine("Bicycle owner is {0}.", bicycle.Owner);
C>

C>

      string? F() { return ""; }


      public int M2()
      {
        if (F() is object o && o.GetHashCode() == 1)
        {
          return 1;
        }
        else if (F() is {} s)
        {
          return s.Length;
        }
        else
        {
          return 2;
        }
    }

    public int M2() 
    {
        return F() switch
        {
          object o when o.GetHashCode() == 1 => 1, // && или and не подходят
          {} s => 1,
          _ => 2         
        };
    }